Doesn´t sync Cassandra all nodes if the network is up again? I think this was one of the reasons, storing a timestamp at every key/value pair? So i think the response will only temporary be 11. If all nodes have synct it should be 12? Or isn´t that so?
greetings André 2010/11/22 Samuel Carrière <samuel.carri...@gmail.com> > >Cassandra can work in a consistent way, see some of this discussion and > the Consistency section here > http://wiki.apache.org/cassandra/ArchitectureOverview > > > >If you always read and write with CL.Quorum (or the other way discussed) > you will have consistency. Even if some of the replicas are temporarily > inconsistent, or off line or whatever. Your reads will >be consistent, i.e. > every client will get the same value or the read will not work. If you want > to work at a lower or higher consistency you can. > > > >Eventually all replicas of a value will become consistent. > > > >There are a number of reasons why cassandra may not be a good fit, and I > would guess something else would be a problem before the consistency model. > > > >Hope that helps. > >Aaron > > Hello, > > I like cassandra a lot and I'm sure it can be used in many use cases, > but I'm not sure we can say that we have strong consistency, > even if we read and write with CL.Quorum. > > Firstly, we can only expect consistency at the column level. Reading > and writing with CL.Quorum gives you most of the time > a consistent value for each individual column, but it does not mean if > gives you a consistent view of your data. > (Because cassandra gives you no isolation and no transactions, your > application has to deal with data inconsistencies). > > Secondly, I may be wrong, but I'm not sure consistency at the column > level is guaranteed. Here is an example, with a replication > factor of 3. > Imagine that the current value of col1 is 11. Your application tries > to write "col1 = 12" with CL.Quorum. > Imagine the write arrives to node 1, but that the new value is not > transmitted to nodes 2 and 3 because of network failures. So > the write fails (this is the expected behaviour), but node 1 still has > the new value (there is no rollback). > > Then, imagine that the network is back to normal, and that another > client asked for the value of col1, with CL.Quorum. Here, > the value of the response is not guaranteed. If the client asks for > the value to node 2 and node 3, the response will be 11, but > if he asks to node 1 and node 2 or 3, the response will be 12. > > Am I missing something ? > > Samuel >
